1. Field
One embodiment of the invention relates to a keyboard having glowing keytops, and a lighting module for a keyboard in which a light source is incorporated into a membrane switch operated by keytops. The embodiment of the invention also relates to an electronic apparatus such as a portable computer having a glowing keyboard.
2. Description of the Related Art
A portable computer, which is an example of an electronic apparatus, is equipped with a keyboard via which information such as numbers and letters is manually input by the operator. The keyboard includes a plurality of keytops and a membrane switch. The membrane switch has a plurality of fixed contacts and a plurality of movable contacts. The fixed contacts and the movable contacts each correspond to the keytops.
When the operator depresses a desired keytop with a fingertip of his/her hand, a fixed contact and a movable contact corresponding to the depressed keytop contact each other, and the membrane switch is closed. Thereby, an input signal indicating that the keytop has been pressed is sent to a keyboard controller from the membrane switch.
When the operator operates the keyboard in a dark environment or a dim room where enough illumination light is not provided, it makes it hard for the operator to recognize the keytop that should be operated. This worsens the operability of the keyboard, which can become a cause of an input error.
To improve this, in a keyboard disclosed by Jpn. Pat. Appln. KOKAI Publication No. 2002-260478, for example, a light-emitting means for lighting up keytops is provided below the keytops. A conventional light-emitting means is formed of a backlight sheet having a light-emitting diode.
The backlight sheet includes a lightguide plate having a light-diffusing layer, and a reflective sheet laminated on the lower surface of the lightguide plate. The light-emitting diode as a light source is mounted at one end of the lightguide plate.
The backlight sheet is laminated on the lower surface of a substrate supporting the membrane switch and the keytops. The light emitted by the light-emitting diode travels in the lightguide plate while being repeatedly reflected, and is emitted through the light-diffusing layer and the reflective sheet from the upper surface of the lightguide plate.
The light emitted from the upper surface of the lightguide plate penetrates the substrate and the membrane switch of the keyboard, and is led to the keytops. The keytop has optical transparency at least in the letter part indicating the function of the keytop. Therefore, a part of light emitted toward the keytop from the lightguide plate penetrates the letter part of the keytop, and thereby the letter glows.
As a result, the operator can recognize the kind and the function of the keytop even in darkness or a dim environment. This prevents erroneous operations of the keyboard.
In a conventional backlight sheet, a light-emitting diode is mounted at one end of a lightguide plate. Such a configuration requires an exclusive wiring part such as a flexible printed wiring board supplying an electric current from a power supply to the light-emitting diode. This increases the number of parts forming a keyboard, and the cost of the keyboard. Furthermore, since the backlight sheet is laminated on the lower surface of a substrate of the keyboard, it cannot be avoided that the backlight sheet projects into the lower part of the keyboard. This results in increase in overall thickness of the keyboard including the backlight sheet. Therefore, a recent demand for forming a keyboard flatly and compactly cannot be satisfied.